First-year dispersal in white-tailed eagles Haliaeetus albicilla

Abstract

Dispersal is a key process affecting the dynamic and genetic structure of populations. To increase our knowledge on first-year dispersal in the white-tailed eagle (WTE), 35 nestlings in the Czech Republic, Hungary, and Austria were equipped with GPS/GSM loggers while on the nest between 2016 and 2019. Twenty-nine individuals surviving until March 31 were used to assess post-fledging areas, first-year dispersal distance and direction, temporary settlement areas, and habitat selection. The first flight from the nest was observed between May 19 and July 8. Start of dispersal from post-fledging areas occurred between July 1 and November 14. Post-fledging areas were significantly larger in males (p = 0.001, median 1236 km2, n = 15) than females (median 139 km2, n = 12). Maximal dispersal distance ranged from 93 to 433 km from the native nest (median = 187 km) and did not correlate with Simpson’s Diversity Index computed for habitats in individual 100% minimum convex polygons (MCP). Median sizes of minimum convex polygons were 26,888 km2 for 100% MCP and 13,376 km2 for 95% MCP (n = 29). Median sizes of kernel density estimates (KDE) were 3393 km2 for 80% KDE and 1137 km2 for 50% KDE. After start of dispersal, young WTEs returned to the proximity of the parental nest for night roosting sporadically. No sex-specific differences in dispersal distance were recorded. While young individuals from the three subpopulations are likely to occur in the same area during the first year of life, future nesting site identification will enable us to assess real gene flow and the connectivity level among them. As this study has illustrated, future conservation efforts to protect young WTEs will require cross-border cooperation.